This invention relates to archery bow limb construction and particularly to laminated bow limbs having a core strip to which tensile and compressive strips are glued to opposite sides thereof.
It has been the practice for a long time to face and back archery bow limbs with strips of material having higher tensile and compressive strengths than the material of which the limbs were ordinarily constructed, usually wood of some kind. More recently, laminated bow limb construction has often considered in gluing a strip of composite material usually composed of glass, graphite or other suitable fibres in a matrix of hard sythetic resin to the back and face of a solid or laminated hard wood core strip.
It has been found that a substantial reduction in bow limb inertia resulting in a substantial increase in arrow velocity is achieved by reducing the weight of the core strip. Applicants have substantially reduced the weight of the core strip while retaining adequate physical properties for the purpose by constructing the core of a material known as "syntactic foam" which consists of a plurality of hollow micro spheres of less than 100 microns in diameter in a matrix of hard synthetic resin. The relative volume of hollow spheres is such as to attain a density of the "syntactic material" which is substantially less than any solid or composite hardwood core.
It was also found that in addition to reducing the weight of the core strip and therefore the inertia of the bow limb in this manner, that the hollow micro spheres in the core material also function as microscopic shock absorbers to dissipate energy of impact and therefore the syntactic material has a relatively high resistance to impact which renders the material peculiarly suitable to bow limb construction. Archery bow limbs in normal usage are subjected to relatively high impact stress every time an arrow is shot and the bow limbs approach a braced position.
In the case of heavier hunting bows it is contemplated employing, in addition to the hollow micro spheres, reinforcing fibres for further enhancing the physical properties of the syntactic material while maintaining a density substantially below that of any solid or laminated hardwood. Moreover, when molding the cores the rolling action of the spheres helps distribute evenly the hollow micro spheres and fibres in the very thin tip ends of the tapered cores.